The intra-articular disc of the temporomandibular joint (TMJ) serves to improve joint fit, facilitate movements, distribute joint loads, protect articular surfaces, and spread lubrication. Yet relatively little is known about its function in vivo and about the relationship between its chemical structure and mechanical behavior. By examining the properties and characteristics of the disc in normal and nonsurgically altered conditions, this study will address these issues. The aims are (1) to examine the in vivo deformations of the disc during function by implanting a strain transducer into the lateral aspect of the disc, (2) to assess the material properties of the disc by in vitro uniaxial tension tests, (3) to investigate sulfated GAG type, concentration, and synthesis in the disc by electrophoresis gel, liquid scintillation counting of [35S] labeling, and DMB analysis, and (4) to inspect the collagen fiber orientation of the disc. Experimental subjects, miniature pigs, will randomly be placed in groups to function as controls or to wear occlusion altering splints for 2 months. Because the more anterior location of condylar loads should cause disc remodeling, the TMJ discs of animals subjected to anterior displacements of the mandible are expected to show (1) a decrease in the anteroposterior deformation of the intermediate band during function; (2) a diminution of viscoelastic behavior, a higher elastic modulus and a lower ultimate strength point; (3) an increase in GAGs and a size shift in biglycan in the anterior bands and a decrease in proteoglycan synthesis in the intermediate band; and (4) a multidirectional collagen fiber pattern in the intermediate band and a more parallel fiber arrangement in the anterior band. In the long term, the results of this study will provide information needed to formulate computer models of disc behavior and will shed light on the role of the disc in temporomandibular disorders.